I have recently started playing Pokémon GO, and I just reached level 13. But suddenly, every pokémon I catch seems to run away (I mean literally all of them) and I can't use gyms or pokéstops. I really need a fix on this as I enjoy the game very much!
Have you been GPS Spoofing or using 3rd-party map applications such as PokeRadar to assist you in your gameplay? Because these things are cheating, and Niantic may ban you if caught. If you are "Banned", you can still "play" the game, but all pokemon will flee from you, and gyms and pokestops will not work. Sounds an awful lot like what you're experiencing.